To analyze a number of liquid samples in a predetermined order by an analyzing system, it is necessary to change the channel in a “sample introducing device”, i.e. a device for introducing samples into the analyzing system. FIG. 1 schematically shows a typical channel system for liquid samples in an analysis of the liquid samples. The sample introducing device 30 includes sample containers 31, each of which holds a liquid sample, a washing liquid container 32 holding a washing liquid, a sampling needle 33, an injection port 34 and other components. The injection port 34 and the liquid contained in the washing liquid container 32 are respectively connected, via a channel-switching valve 1, to a channel extending from a liquid-feeding pump 20. The liquid-feeding pump 20 supplies a mobile phase from a mobile-phase container 10 to the sample introducing device 30. Inside the sample introducing device 30, the channel-switching valve 1 is operated so that a number of liquid samples are sent into the channel and carried to an analyzing system 40 in a predetermined order.
The sample introducing device 30 receives high-pressure liquid from the liquid-feeding pump 20. Taking this into account, a valve as shown in FIGS. 2A and 2B is used as the channel-switching valve 1, in which a disk-shaped rotor 2 provided with channel grooves is mounted on a disk-shaped stator 3 having a plurality of ports and is rotated while sliding on the stator 3. In this channel-switching valve 1, the stator 3 has a plurality of ports a-f (only the ports a and d are shown in FIG. 2A) each of which can be connected to one of the channels, with the slidable rotor 2 being mounted on the stator 3. The rotor 2 is pressed onto the stator 3 by a shaft 5 supported by an elastic member, such as a spring (not shown), so as to maintain the liquid-tightness of the channel. FIG. 2B is a plan view of the contact surface 4 of the rotor 2 in contact with the stator 3. The openings of the ports a-f of the stator 3 are also shown. The contact surface 4 is provided with arc-shaped channel grooves X, Y and Z for connecting the openings of the ports a-f A channel is formed by connecting the channel groves X, Y and Z to the openings of the ports a-f. The combinations of the ports connected by the channel groves X, Y and Z can be changed by revolving the rotor 2 around the rotational center 6. Thus, the channel can be switched. Typically, the stator 3 is made of a metal or ceramic, while the rotor 2 is made of a resin.